1. Field of the Invention
This invention relates to disc filter assemblies and more particularly to a fabricated central shaft supporting the disc filters, wherein the central shaft has mounted thereon pipes which have a trapezoidal cross-sectional shape.
2. Description of the Prior Art
Disc filter segments have long been used in conjunction with a rotatable central core for filtering taconite slurry. Disc filter segments are wedge shaped and have a hollow interior. The disc filter segments are securely mounted about the core. The core rotates to sequentially submerge the successive segments in a slurry. A vacuum draws the slurry filtrate into the filter segments. The filter segments are operably connected to a conduit within the central core. The filtrate enters the conduit and is drawn out through the ends of the central core.
The use of powerful vacuum pumps creates problems when a filter segment tears to allow unfiltered slurry containing iron ore filings, coal particles, or other industrial particulates through the filter. The particulates are drawn into the conduit and cause erosion therein. The erosion is particularly severe on the interior surface of a conduit opposite the aperture leading from the filter segment.
Various modifications and improvements to the disc filter have been sought to improve the reliability of the central core and to lessen the cost of the repair and replacement due to the wear and tear of the central shaft.
In one attempt to solve the problem of erosion, the central core was made from a solid cylindrical piece of cast iron. The conduit passageways are radially placed around an axis of the core with a substantially thick iron wall surrounding each conduit. The passageway through the core is bored and is cylindrical in shape. The central area of the iron core is hollow to provide a lighter weight iron core. When the passageway is eroded, the cylindrical passageway is rebored a little wide. However, erosion eventually eats away to the hollow central area of the core, causing a break in the passageway. The break in the passageway renders the passageway inoperative and causes a general loss of vacuum efficiency.
Replacement of the eroded iron core is costly and time consuming. High cost replacement of the iron core is due to the fine machining that is required to have different sections of the iron core aligned correctly with other sections so that all sections rotate around their axes without wobble. The time required to replace the iron core is significant since the whole filter disc assembly must be disassembled and reassembled onto the new iron core.
Since replacement of the iron core is expensive and time consuming, the repair is often made to the core by merely plugging up the passageway at the point of erosion. The repair by plugging renders at least one filter segment inoperative since the plug blocks any passage from the filter segment to the conduit. The iron core is used until a number of filter disc segments become inoperative due to a plurality of plugs sealing off major portions of the passageways. The economics of replacing an iron core demands that a crippled iron core be used long beyond the point where the iron core is being used efficiently.
Another attempted solution to erosion problem is disclosed in the U.S. Pat. No. 2,894,632 issued to R. B. Myers on July 14, 1959. Myers discloses a modified filter segment integrally connected to a pipe segment which is rotatably mounted onto central shaft. If the filter segment is ripped or the pipe segment is worn, only that section need be replaced. However, the Myers reference is not compatible with the conventional disc filter segments because the pipe segments are integrally formed with the filters.
Another proposed solution to the erosion problem is disclosed in the U.S. Pat. No. 3,659,716 issued to Peterson et al on May 2, 1972. Peterson discloses a filter disc central core assembly having a tubular shell and a plurality of longitudinal pipes welded to the interior surface of the shell. The pipes have a rectangular cross-sectional shape having apertures intervally spaced along the length thereof and have reinforced surfaces at the opposite sides of apertures in the pipes. Removable castings are attached to the pipes and extend outwardly from the pipe apertures. The castings have angled walls which receive the blasting force of the filtrate. The removable castings would have to be replaced at regular intervals of time. The castings are adapted to be attached to conventional disc filter segments. The reinforced surface opposite the aperture and the castings are adapted to be attached to conventional disc filter segments. The reinforced surface opposite the aperture and the castings is designed to receive the force of the flow and increase the time interval for necessary replacement of the central core.
The use of rectangular shaped pipes or circular shaped pipes mounted circumferentially about a tubular shell or mandrel unnecessarily confines the cross-sectional area of the passageways. The confinement of the passageway causes the vacuum to create a greater suction therethrough which increases the wear and decreases the durability of the pipes.